Lightweight trucks or pickups having an open box are ideal vehicles for hauling articles to and fro, as the box of the pickup contains a relatively large storage area. In order to protect articles from weather and to prevent the theft of these articles from the open box of the pickup, pickup owners frequently place a cover known as a "topper" over the box of the pickup. The topper provides a closure over the box of the pickup with the topper usually extending upward in height to the top of the cab. The amount of head room beneath the topper is limited, so if a person wants to set an article in the front of the pickup box, he or she must bend over or crawl to move the article to the front of the box as one cannot place articles over the sides of the pickup box when the topper is in place. The present invention provides a kit for making an extendible platform from conventional materials to provide a low-cost extendible platform that enables a person to cantileverly extend a loading surface from the rear of the pickup box to enable articles to be loaded onto the extendible platform and then to slide the platform to the front of the pickup box while using the tailgate of the pickup as a cantilever support.